A device for retaining a mercury source in the discharge space of a low-pressure discharge lamp is disclosed. The mercury source retaining device comprises a holder, which has an inner space communicating with the discharge space and a receiver opening for receiving a mercury source. The retaining device further comprises resilient clamping means for clamping the holder in a tubular space segment of the discharge space and resilient retaining means at least partially blocking the receiver opening. The resilient retaining means are adapted for allowing a passage of the mercury source in a direction towards the inner space of the holder, but block the movement of the mercury source through the receiver opening in a direction out of the holder.